Many veins of the human body or animals include natural valves that aid in the return of blood flow toward the heart. These natural valves may prevent blood from pooling in the lower legs and feet. The proper function of these venous valves is especially important during standing or sitting when the weight of blood in the vein can slow blood flow toward the heart. Problems can arise when these venous valves fail to function properly. For example, venous valves can become incompetent or damaged by disease such that the backflow of blood is not prevented. When this occurs, blood pressure builds up and the veins and their valves become dilated, particularly in the lower extremities. If enough pressure builds up, the condition of venous insufficiency may develop. The severity of this condition is substantial, resulting in swelling, extensive pain, deformities, and, in the most severe cases, the development of ulcers can occur. If these ulcers become infected, amputation may ultimately be necessary to save the patient's life.
Currently, there is no proven cure for venous insufficiency. Basic treatments include elevation of the legs or the use of compression stockings. If surgery is determined to be necessary, vein stripping is typically performed, which involves the removal of the incompetent or damaged vein(s). Other surgical methods involve valvular reconstruction or transplantation.
The development of artificial and biological valves has been employed in an attempt to return normal pressure to the veins. There are a variety of these valves described in the art, which are generally designed to allow normal flow of blood back to the heart, while preventing retrograde flow. However, blood flow within a vein is intermittent and bidirectional, subject to constant fluctuation in pressure and volume. As a result, the shape of a lumen of a vein can undergo dramatic dynamic change resulting from these varying blood flow velocities, pressures and volumes therethrough. Many design considerations, consequently, regarding artificial valves for the venous system are taken into account. One primary consideration includes the ability of the frame and the valve to conform to the dynamic fluctuations in the shape of the lumen of the vein. Another primary consideration is the ability of the valve to be implanted in a body vessel having a variable diameter along the length of a site of implantation, or a branched body vessel site of implantation.
What is needed is an intraluminally-placed valve prosthesis, including a frame and valve, or closure member, that is compliant to be delivered percutaneously and, upon implantation, configured to prevent migration within the body vessel and minimize irritation of the body vessel. In addition, there remains a need for a valve prosthesis to conform to the changing shape of the lumen of the vein. There also remains a need for valve devices having a support frame configured with a radial strength to maintain patency of a body vessel while supporting a means for regulating fluid within the body vessel.